Many sheet-like materials are stored, transported, and supplied in the form of rolls, where the sheets are rolled up around a bobbin. These rolls are commonly known as “roll stock.” Materials sold in rolls include fabrics, plastic films, paper products, aluminum foils, nets, yarn and wire products, and others.
Bobbins are generally cylindrical tubes and the most common types are made of cardboard of a great variety of thicknesses and strengths. To prepare roll stock, the bobbin is placed on a mandrel and the sheet material is wound onto it. Similarly, the roll stock may be placed onto a mandrel for dispensing the sheet material.
Cardboard, even in the form of rolls, is not a particularly strong material and can fail under circumstances in which it is bent, crushed and even cut into multiple pieces. As the rolled sheet material is wound more tightly around the bobbin, or where a heavier sheet-like material is used, the pressure on the bobbin increases, requiring a stronger bobbin to withstand the higher pressure. A common technique to increase the strength of a cardboard bobbin is to increase its wall thickness. In the case of wound material such as netting, not only is a bobbin subjected to greater pressure due to the heavy nature of the netting, but, by virtue of its make-up, netting applies a non-uniform concentrated pressure on certain points along the bobbin length. Cardboard bobbins are not sufficiently strong and resilient for supporting all sheet stock material. Moreover, when long rolls of material are stacked on top of one another, in transport or storage, the cardboard bobbins are subject to crushing. Therefore, the thickness of a cardboard bobbin is dependent on the particular type, length and width of the material to be rolled thereon, the circumstances of its use, as well as the length and diameter of the bobbin itself.
Cardboard bobbins are particularly vulnerable to water and humid conditions and as such must be protected from wet weather conditions as well as damp conditions present during storage, transport, and dispensing. Cardboard bobbins used in roll stock have limited reuse because of their susceptibility to damage from rain and humidity and from physical handling in transport, and because of the cost for protected storage space for bobbins between uses. Also, stronger cardboard bobbins, which may include additional cardboard layers for added protection from these damage issues, increase the expense of bobbins while not necessarily assuring reuse.
Other bobbins in common use are extruded PVC plastic tubes. These have some advantages over the cardboard bobbins in that they are largely weatherproof and can be manufactured by extrusion to infinite length and thereafter can be readily cut to different sizes as required. Their disadvantage is that they tend to crack when subjected to stress, particularly under low temperature conditions, and they are expensive to manufacture. Older plastic bobbins are also particularly brittle, especially if exposed to temperature extremes or sunlight.
Common cardboard bobbins presently in use comprise a series of paper layers, glued one layer to the next. If a particular area along the length of the bobbin must possess increased strength to support a greater weight of rolled material, the entire bobbin must be strengthened. This is because additional layers of cardboard needed to increase the strength of that particular area, must be added to the entire length of the bobbin, even if the area which requires the increased strength is only a small percentage of the overall length of the bobbin.